1. Field of the Invention
The invention relates to a projection optical system having comparatively long component operating life and excellent display contrast and relates to a light amount adjusting component adapted to the projection optical system.
2. Description of the Related Art
Referring to FIG. 1, a conventional projection optical system 100 includes a light source 102, a color wheel 104, an aperture disk 106, a light integrator rod 108, a digital micro-mirror device 110, a condenser lens 112, a reflective mirror 114, a relay lens 116, and a projection lens 118. The aperture disk 106 is disposed between the color wheel 104 and the light integrator rod 108 and has a slot S. Referring to FIG. 2, since a width of the slot S changes monotonically along an extension direction of the slot S (the width of the slot S decreases in a clockwise direction), when the aperture disk 106 is actuated by a step motor 122 to continually rotate on its axis, an overlap area between the slot S and a light incident surface 108a of the light integrator rod 108 gradually varies to change the amount of light entering the light integrator rod 108 and the projection lens 118. Since a projected black color becomes darker as the amount of light entering the light integrator rod 108 is reduced, the control of the amount of light permits a higher ratio of a projection device's brightest white to its darkest black and thus improves its display contrast.
Typically, a conventional aperture disk 106 is made of aluminum alloy or stainless steel, and thus it has a highly polished surface. When the aperture disk 106 rotates to a position where a light-transmitting portion of the slot S relative to the light incident surface 108a is comparatively small, the aperture disk 106 blocks most of light ready to enter the light integrator rod 108. In that case, the polished aperture disk 106 is subjected to intensive illumination to cause a sharp increase in temperature and liable to be burnt out. Further, the light reflected back to the light source 102 by the polished aperture disk 106 may cause an excessive rise in lamp temperature to fail to maintain a proper range of operating temperature of the light source 102.